Syntax:
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PURE [type-spec] FUNCTION function-name( [ dummy-arg-name-list ] )
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PURE functions have no side effects
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Syntactic constraints:
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Global variables and dummy arguments cannot be used in any context that may cause the variable to become defined
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Left hand side of assignment
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DO index, ASSIGN, ALLOCATE
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Actual argument with INTENT(OUT)
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Targets of pointer assignments (due to later use of pointers)
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Full list of restrictions is too long to fit on this slide!
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No external I/O or file operations
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Only inherited distribution/alignment of dummies and locals
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Intrinsic functions are PURE
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